The present invention relates to safety devices used in cooking or other activities involving hot surfaces, and in particular it relates to safety devices which alert someone that the surface of a stove or other appliance or device is too hot to touch. The present invention also relates to detachable heat alert safety devices for any hot surface.
With respect to stoves and related appliances, various kinds of stovesxe2x80x94electric, gas, smooth cooktop using glass or metal topsxe2x80x94and toaster ovens are well known to be used for heating food. In addition, xe2x80x9cmobile stove-type appliancesxe2x80x9d such as hot plates and warming trays are well known to be used for heating food. Each of these kinds of stoves and xe2x80x9cmobile stove-type appliancesxe2x80x9d present a safety problem since the heating elements of the stove are hot during the cooking process and remain hot well afterwards. During the cooking process, the safety problem caused by touching the heating element is mitigated somewhat by visual inspection of the stove. With a gas, electric or smooth top stove, for example, the presence of a pot or other utensil on top of the stove might alert someone to the fact that the stove appears to be in use for cooking and therefore too hot to touch. Even the presence of a pot or other utensil is not a reliable clue, however, since people tend to leave tea kettles on their stove perpetually. When the cooking process has ended, however, it is generally impossible to detect that the heating elements of the stove remains hot and would burn the skin of anyone who touched them. There is no visual or other clue that the stove is hot.
To some degree, adults have developed an inherent caution when approaching stoves because of their experience and knowledge in dealing with such safety problems. This inherent caution, however, does not obviate the need for a device that warns the adult when touching the stove would be dangerous. Moreover, children, and particularly young children, usually have not developed such a watchfulness and there has long been a need for a device that can prevent burn accidents to children who may inadvertently touch a stove that is hot, especially when the stove remains hot well after the cooking process has ended.
Furthermore, the reduction in the size of modern kitchens has led the occupants of modern apartments to make use of the stove as an extension of the counter top adjacent the stove as a resting places for large items that have been carried into the kitchen area. An example of such items is heavy bags of groceries brought into the kitchen. There is an urge to set the bags down on the nearest flat surfaces, which may be the top of a stove adjacent a counter top. This is particularly true for those stoves that are smooth on top, such as smooth cooktops. In general, the top surfaces of modern kitchen stoves are increasingly flat, especially the top surfaces of smooth cooktops. These factors have only increased the danger to adults when the top surfaces of stoves are used as a resting place for packages, such as groceries brought into the kitchen.
Smooth cooktop stoves presently are also dangerous if touched on their top surface when they are still hot, even after use. These smooth cooktop stoves, or xe2x80x9csmoothtopsxe2x80x9d as they are sometimes called, utilize as the heating element separate areas on the top surface of the stove (at the same location that gas stove would have burners) which are made of glass. Under each area, usually circular, is a strong light source, such as a halogen lights. The light source projects the light upward to the surface area of the smoothtop""s heating elementxe2x80x94the glass area on the top surface of the stove. Since the glass area is coated on its bottom with a dark coating, when the light strikes it, the heat from the strong light is absorbed by the glass area and these glass surfaces form each heating element of the stove.
Another variation of the smooth cooktop is the use of a xe2x80x9cribbon heating elementxe2x80x9d where the smooth glass surface is heated by a coiled electric circuit called a xe2x80x9cribbon elementxe2x80x9d just underneath it instead of by a halogen light source. The heat is transmitted directly upward so that only the heat element itself gets hot and the rest of the cooktop surface remains cool. In some cases, the ribbon heating element also has another feature whereby the heating element is made of two concentric circles so that the option exists of two sizes of the heating element to match the two different sizes of the pans that need to be heated. This new technology does not solve the problem of warning adults and children that the heating element should not be touched when the cooking process has ended. If anything, it generates the additional hazard that someone can be lulled into touching the heating element after thinking the heating element is cool since the surface right adjacent to it is indeed cool.
Some of these problems have been addressed in earlier patents, through use of thermochromic inserts or overlays. Thermochromic materials are those such as some liquid crystals which change color when passing through a given temperature range, and are now familiar from use in inexpensive items, like temperature indicating refrigerator magnets or stick-on aquarium thermometers.
These devices however still suffer from some drawbacks. Flat appliable thermometers tend to be made of plastic, and would melt or be destroyed at the temperatures reached by a kitchen oven. Higher temperature chemical temperature indicating systems are known, such as the semiconductor cadmium sulfide, but must either be included as inserts in original equipment manufacturing, or fired on as a vitreous ceramic. Materials which are both capable of resisting high temperature and are transparent, or which are themselves thermochromic, are brittle, and so unsuitable for forming in thin flat removable displays, which makes it difficult to attach these materials to an existing surface, the way refrigerator magnet thermometer is attachable.
In an additional drawback of the prior art, flat indicators, embedded in or applied to a flat surface, are necessarily only usefully visible through a limited viewing angle. It is readily shown through trigonometry that if an observer is offset an angle xcex1 from the vertical or normal to a surface, which offset is also referred to as the angle of incidence, the apparent area of objects on the surface will be reduced by a factor of cos(xcex1): Axe2x80x2=Acos(xcex1). For example, if an observer is offset 60xc2x0 from the vertical, i.e., at a 60 degree angle of incidence, viewing a surface from 30xc2x0 to the surface itself, the apparent size of objects on the surface is reduced by cos(60)=xc2xd. For an observer at an angle of incidence of 80xc2x0 the apparent size has shrunk to less than 18% of the actual size; and at 85xc2x0 apparent size is less than 9% of actual. An angle of incidence approaching 90xc2x0 from the vertical is known as a grazing angle. At grazing angles a flat indicator on the surface clearly approaches zero apparent area, and is completely invisible to the observer.
A second problem that arises from looking at something at an angle of the line of sight is specular reflection. Specular or mirror reflection is the reflection of light rays hitting a flat surface with a reflected ray having an angle of incidence equal to that of the incident ray. For most surfaces specular reflectance increases with angle of incidence, so that more ambient light is reflected to a viewer at larger angles of incidence of the line of sight. This effect wipes out the contrast of a display, so that the display cannot be read at large angles, even if the apparent area of the display were otherwise large enough. Depending on the type of materials used, the loss in visibility at a given display angle may be worse than that predicted by apparent area alone. Liquid crystals for example show a contrast with background notably affected by viewing angle, and readability of a liquid crystal display may be degraded at lower angles of incidence than other kinds of display.
In consideration of these two effects, loss of apparent viewing area and increase in specular reflection, flat warning devices are mainly suitable for surfaces usually seen from small angles of incidence. Examples of such surfaces are vertical surfaces near eye-level, like a door of a cabinet mounted oven, or horizontal surfaces significantly below eye-level, like a stove top surface considered in relation to a typical adult height.
However, for a child an ordinary stove top may be near or even above eye level, while small hands can nonetheless reach over the top of a stove to touch dangerously hot surfaces. Similarly, even for an adult some vertical surfaces such as an oven door, may be below eye level, and hence only visible at a large angle of incidence. This would occur while a user is standing at the stove and reaching down to open the oven door. A flat indicator therefore will not be prominent or attention getting in these situations, and may even be invisible to a user.
With respect to toaster ovens, because of the mobility of the unit the danger of touching the window of a toaster oven exceeds that of the typical immobile oven. The toaster oven can be placed on a counter top or other portion of the kitchen not directly in the xe2x80x9ccooking centerxe2x80x9d. Consequently, an adult and especially a child, or the elderly, is not likely to remember not to touch a window of a toaster oven when it is off (soon after it had been on). In addition, the door of a toaster oven can be left open and jut out further toward someone in the kitchen.
Presently, in order to address the danger of touching a hot xe2x80x9csmoothtopxe2x80x9d stove, such stoves generally have several light indicators, each one corresponding to each heating element, all located in small one rectangular area on the surface of the cooktop. The light indicators remain lit for a certain length of time after the stove""s heating element is turned off in order to deter someone from touching the heating element when it is still hot, although xe2x80x9coffxe2x80x9d. Unfortunately, this attempt to address the danger of touching a hot stove of the smooth cooktop variety is insufficient as a warning system (putting aside the fact that the light indicators are designed only for the smooth cooktop variety stoves to begin with and not for gas and electric coil stoves).
A quick glance at the group of light indicators would not be sufficient to warn the average adult, no less children or the elderly, that a particular heating element is too hot. This is because the group of light indicators do not immediately tell someone which heating elements correspond to which light indicators. At a minimum, several seconds of concentration are needed in order to determine from the light indicators that are xe2x80x9conxe2x80x9d, which heating elements are too hot to touch. Many adults, and certainly most children, cannot afford those seconds of deduction since their desire to touch the stove is immediate. In addition, an adult carrying groceries into the kitchen and looking for a counter top to place them on or a child running into and playing in the kitchen are even less likely than the average adult or child to take the time to engage in a several second thinking process. Accordingly, the child or the adult will be inadequately warned about the danger of being burned. With this in mind, it is no surprise that a 1997 industrial design exhibit at the Cooper Hewitt (Smithsonian) in New York demonstrated that over 69% of adults can not match the control knob with its corresponding burner (i.e. heating element) on a stove.
There is also not presently known any effective warning method for the vertical surfaces of oven windows, including the windows of wall ovens, regular ovens and toaster ovens, and especially when such vertical surfaces are not at or near eye level for a user, as mentioned above. This is particularly important since when the oven is turned off, the oven window remains very hot even though it appears that everything is off.
While devices that make use of liquid crystal compositions are known to indicate the surface temperature of an appliance, these devices are not designed to warn someone of the danger of touching hot stoves. For example, U.S. Pat. No. 3,827,301 to Parker discloses an apparatus for indicating the temperature of a surface of an appliance. It has a first portion in contact with the appliance surface or connected by copper wires or heat pipes to the appliance surface. It has a second portion, a poor heat conducting member in heat exchanging relationship to the ambient environment, that has bands of liquid crystal material extending away from the first portion thereby creating a temperature gradient extending away from the surface of the appliance.
Devices such as disclosed in Parker that provide temperature determinations are not adequate for instantly warning a child or even an adult that the heating element of a stove is too hot to touch for one thing because quantitative temperature determinations are inadequate to provide the immediate warning that is necessary. Moreover, the device of Parker and other liquid crystal compositions are not specifically suited to be manufactured as part of a stove. In addition, these devices are not suitable as attachments to stoves and certainly not as attachments to a smooth cooktop stove.
The present invention is also applicable, not just to stoves and related appliances, but to any other surface that one may need to be warned that it is hot. There are numerous devices whose surfaces become hot and remain hot even after the device has been shut off either electrically or otherwise. For example, a radiator cap becomes hot and remains hot for a period when the vehicle and radiator are shut off. Also, any kind of piping that is a conduit for hot liquids is an example of a surface that one may need to be warned that it is hot. Other devices having hot surfaces include hot surfaces on fireplace doors, flat irons, chafing dishes, coffee urns, heating pipes, home radiators, glue guns, oven doors, portable heaters of the electric, oil and ceramic disc type, kerosene lamps, kerosene heaters, barbecue grills of the electric, gas or charcoal type, electric woks, electric skillets, deep fryers for home or commercial use, heat lamps in self service cafeterias and salad bars, saunas including the metal box that generates and/or controls the heat, rotisseries, indoor grills whether gas or electric, tea kettles, wood burning stoves, hot electric rollers, hot wax holders used for beauty treatments, bonnet type hair dryers, synthetic braid trimmers, curling irons, portable generators, steam cleaners especially such as in dry cleaning facilities, hot water pipes that are exposed, hot water heaters, furnaces, warming trays, light fixtures such as halogen lamps, popcorn makers (especially commercial ones), toasters, cappucino and espresso makers, autoclaves used to sterilize instruments in a medical setting, movie projectors and other such hot surfaces. These and other hot surfaces are exposed to children, maintenance works and ordinary adult users.
Accordingly, there is needed a versatile, easily movable and mountable, removably attachable and detachable, and effective, convenient and easy to manufacture device for warning adults, workers and children instantly when any kind of surface, whether it be a stove of any kind or any other surface, is too hot to touch. There is also a need for such a device that is both capable of installation on a previously purchased stove of any known type, including cooktops, electric and gas stoves, and one that is also capable of being manufactured as part of the stove by stove manufacturers. The present invention addresses and satisfies all of these needs and provides other advantages.
There is also a need for an effective, convenient and easy to use, and detachable heat alert safety device that is easily read and understood for warning adults and children when any surface is too hot to touch. Such a device should ideally be positionable at a variety of heights or positions so that it can be custom tailored for children of different height.
Importantly, moreover, there is a need for a heat alert safety device that is versatile enough to be easily positioned on a hot surface and yet be able to be easily removed thereafter when it has served its purposexe2x80x94either with respect to that surface or it has served its purpose with respect to that particular individual or it has served its purpose for that individual for that particular momentxe2x80x94and then be repositioned elsewherexe2x80x94either on another hot surface of another object or another surface of the same object or even another portion of the same surface of the same appliance. This is necessary because in order for the heat alert safety device of the present invention to be effective it has to be visible (or at least discernable) and in addition it should be discernable and effective for children, and since children of different ages are of different heights it is advantageous to be able to attach the device to. It is also necessary because a particular individual may decide to relocate the heat alert safety device when a different appliance is used or when a different portion of a kitchen counter is used, or when any other object with a hot surface is activated. It should be noted that by xe2x80x9cactivatedxe2x80x9d is included situations when an object is xe2x80x9chotxe2x80x9d a certain amount of time after the source of the heat was xe2x80x9conxe2x80x9d and it is of course not intended that the device of the present invention is limited to situations when electricity is xe2x80x9conxe2x80x9d for an appliance or other object.
In light of the above discussion there is a need for a device which (i) is suitable for temperatures at least up to a high temperature of a gas oven (500xc2x0 F.) (ii) is capable of conveying information at a grazing angle of sight, relative to the surface the device is mounted on (iii) may be detachably mounted on an existing surface. It is believed that no heretofore known product simultaneously meets these requirements. It would also be advantageous if the device were simple and rugged and could withstand chance mishandling or rough treatment.
In the present invention chemical compositions that change color and remain at that color when they reach or exceed a certain temperature (referred to generally herein as xe2x80x9cthermochromic compositionsxe2x80x9d), such as cholesteric liquid crystals or various types of liquid crystal polymers designed to turn color when they reach a certain temperature, and that are shaped in the outline of the word xe2x80x9cHOTxe2x80x9d are embedded in a device attachable to or forming a part of any hot surface such as the top surface of the heating element of stoves so that they change color and instantly alert anyone, including a child, that the heating element of the stove is too hot to touch even when the stove or other device is xe2x80x9coffxe2x80x9d.
The present invention is a lightweight convex button type temperature surface warning device, or xe2x80x9chot buttonxe2x80x9d. The device preferably fits in the palm of the human hand and resembles a campaign button""s outer shape. The device is distinguishable over earlier art in that a warning signal represented by a thermochromic material is visible over a substantially increased arc, at least up to grazing angles with a not surface, whereas at such angles existing flat indicators would be useless. A xe2x80x9cgrazing anglexe2x80x9d is any small angle approximately less than 10xc2x0, and down to and including 0xc2x0. In some embodiments and applications, a warning signal may be visible below a grazing angle, i.e., from an angle of sight below the hot surface. In one embodiment a thermochromic composition is enclosed in an optically clear, physically rugged and convex button or lens, typically manufactured of tempered glass. In another embodiment, the thermochromic composition is embedded in a convex surface of such a button, which in this embodiment may be opaque. The thermochromic composition is however preferably embedded in a back side of the button which is manufactured out of a moderately heat conductive material like glass, to minimize a thermal lag between the protected surface and the indication, whereas a button manufactured out of a good thermal conductor such as aluminum will function satisfactorily with the thermochromic composition embedded in the front surface. The rear surface of the button may be either flat or concave.
In any case the device is entirely constructed out of material able to withstand repeated cycling to a temperature of approximately 500 degrees Fahrenheit or more, and able to withstand rough treatment. The thermochromic material is shaped in a predetermined symbol or shape, such as the English letters xe2x80x9cHOTxe2x80x9d or such letters in another language, or in the background of such a symbol, communicating to a viewer that a surface is dangerously hot. The symbol may also take the form of a exclamation point, an international xe2x80x9cnoxe2x80x9d symbol superimposed a stick diagram of a figure touching a surface, a stylized human face showing shock or pain, a representation of flames, or any other recognizable warning symbol. Preferably the symbol or its background should lie in the color range red-orange-yellow, commonly recognized colors of both high temperature objects and of required caution.
In a further embodiment of such invention, the warning symbol is repeated or a pattern of thermochromic material is extended over a larger portion over a first or rear side of a convex button or lens so that a warning signal is yet more viewable over a wider range of angles from a second or front side of the button. The words xe2x80x9cHOT! HOT! HOT! may for example be repeated in a horizontal strip running across or behind a convex face so that at least one complete word is visible from a larger range of horizontal angles. Alternatively an abstract pattern such as alternating wavy lines or a field of exclamation points, normally invisible and becoming red and black at a predetermined temperature, can be continued across a front or back surface of the button, so that portion of the pattern visible to a viewer on the front side of the button will suffice to convey the warning.
As discussed in the background section, visibility of a flat warning signal is usually unacceptable greater than 70xc2x0 to either side of a normal (perpendicular line) of the protected surface, and rapidly becomes worse as the viewing angle approaches 90xc2x0. The xe2x80x9cviewing anglexe2x80x9d or angle formed with the normal to the surface is also referred to as the angle of incidence, or in particular the angle of incidence of the line of sight. In contrast to a flat panel display, the device of the present invention allows a warning to be communicated to a user at viewing angles up to 90xc2x0 from the vertical, or grazing the surface. The warning signal in some applications will even be visible from slightly beneath the surfacexe2x80x94an angle of incidence greater than 90xc2x0xe2x80x94provided a line of sight exists from the observer to a projecting portion of a display face of the device. The wide range of visibility is achieved by a use of clear material as a convex container for a thermochromic composition, and by an optional tiltable mounting enabling orientation of an axis of maximum visibility to be repositioned. Alternatively the effect is achieved by using a cap of heat conducting and possible opaque material, such as aluminum, with a thermochromic material on or in a convex front surface of the cap. This arrangement is also optionally combined with a tiltable mounting.
The utility of this invention where a person may be tempted to reach around a corner to grasp a handle on a hot surface or when a small hand is attached to a child tempted to reach on top of a stove, will be readily appreciated.
In optional embodiments of such invention a preferred range or solid cone of viewing angles is selectable by pivoting a button element mounted on an end of a stalk. This arrangement is also called a xe2x80x9cmushroomxe2x80x9d arrangement. The stalk in this case is long enough to permit a pivoting through a predetermined range of angles of the head or button without interfering with the protected surface. In cases where the pivot is not used the stalk may be shorter, any length down to a minimum thickness necessary for mounting on a surface.
The hot-button is temporarily affixed to ferrous (magnetic) surfaces by means of high-temperature resistant ceramic magnets, which are usable up to approximately 800xc2x0 F. For yet higher temperatures, such as a side of coal-fired barbeque grills, a high temperature cement is used to permanently attach the button to the surface. Some embodiments may include a metal backing welded to a screw thread or other attachment post, which may be passed through a hole in a metal or glass surface and secured, for example, with a lock-washer and nut.
The unique features of the present invention include the large range of viewing angles achieved by a combination of optical and geometrical means, combined with a temperature service range extending at least to 500xc2x0 F., rendering the device suitable for ovens and other cooking appliances, and visible at a grazing angle to the surface.
For completeness, various other embodiments which were disclosed in my prior application, of which this application in a continuation-in-part, will now be summarized.
In another embodiment described and claimed in my previous patent, U.S. Pat. No. 6,104,007, for use on electric stoves, the device is an improved electric coil whose central area contains the liquid crystals. In a second embodiment for use on smooth cooktop stoves, wall ovens and toaster ovens, the thermochromic display is embedded in the glass areas that form the heating elements of the smooth cooktop stove. As an alternative to the second embodiment, for smooth cooktop stoves, the thermochromic display is in the shape of a ring surrounding the heating element (and visible when pots are placed on the heating element) which ring may have an interrupted area in the outline of the letters xe2x80x9cHOTxe2x80x9d). In a third embodiment for gas stoves also described and claimed in U.S. Pat. No. 6,104,007, the thermochromics are embedded in a recessed disk mounted on top of the central element of the gas stove""s burner. In each embodiment, the thermochromics stay red as long as the temperature they sense exceeds a certain degree Fahrenheit, such as 115 degrees Fahrenheit, which has been found to be too hot to touch. In a fourth embodiment for use on wall ovens and toaster ovens, the thermochromic display is embedded in the glass areas that form the heating elements of the smooth cooktop stove.
In one embodiment described in detail herein, in order too achieve removable attachability and placement, the heat alert safety device is made of two part, a half-dollar disk made of Pyrex and containing the thermochromic composition and an attachment and heat conducting element in a disk in the shape of a dime on the back of the half-dollar shaped disk.
The following important objects and advantages of the present invention are:
(a) to provide a device that instantly warns anyone including a child that the surface of a stove, hot plate, the window of a toaster oven, or other hot surface is too hot to touch,
(b) to provide a versatile heat warning device that can be used for smooth cooktop stoves having any kind of surface including glass or metal and using any kind of technology including electric heating, electric induction and halogen light heating, or can be used for electric stoves, or for gas stoves, for wall ovens, for toaster ovens, for hot plates or for warming trays,
(c) to provide a device visible to the extent of providing a warning through an arc of at least 180 degrees about the vertical to a protected surface,
(d) to provide a heat warning device that is easy to manufacture and that can be either installed onto the stove (or other appliance""s) heating element or can be manufactured as part of the stove,
(e) to provide a heat warning device for stoves that can be calibrated to produce a warning symbol only when a certain temperature, such as 115 degrees Fahrenheit, is reached and that can remain in signaling mode as long as such temperature is exceeded by the appliance surface,
(f) to provide a heat warning device as above that makes use of thermochromics that change color when a certain temperature is reached, such as cholesteric liquid crystals or cadmium sulfide semiconductors designed to change color when a certain temperature is reached,
(g) to provide a heat warning device that is removably attachable to a wide variety of hot surfaces in a very simple manner,
(h) to provide a heat warning device that can is readable by children and whose placement can be adjusted when the child grows taller,
(i) to provide such a heat warning device that can be angled for easier reading on surfaces in out-of-the-way locations such as pipes,
(j) to provide such a heat warning device that contains a magnet or an electrically conductive plastic that makes the device removably attachable to any hot metal, glass or other suitable surface and capable of receiving heat transmitted from the hot surface and transferring it to the thermochromics that change color when a certain temperature is reached and
(k) to provide a heat alert safety device that is readily attachable to and detachable from hot surfaces on fireplace doors, radiator caps, irons, chafing dishes, coffee urns, heating pipes, home radiators, glue guns, oven doors, portable heaters of electric, oil and ceramic disc, kerosene lamps, kerosene heaters, barbecue grills of electric, gas or coal, electric woks, electric skillets, deep fryers for home or commercial use, heat lamps in self service cafeterias and salad bars, saunas including the metal box that generates and/or controls the heat, rotisseries, indoor grills whether gas or electric, tea kettles, wood burning stoves, hot electric rollers, hot wax holders used for beauty treatments, bonnet type hair dryers, curling irons, portable generators, steam cleaners especially such as in dry cleaning facilities, hot water pipes that are exposed, hot water heaters, furnaces, warming trays, light fixtures such as halogen lamps, popcorn makers (especially commercial ones), toasters, cappucino and espresso makers, autoclaves used to sterilize instruments in a medical setting, movie projectors and other such hot surfaces.